1. Field of the Invention
The invention relates generally to structural elements in aeronautical blades, and, more particularly, to structural optimization of rotor and turbine blades.
2. Description of the Related Art
Rotor blades are aerodynamically complex structures that are subjected to intense deflection forces and are thus required to satisfy numerous design requirements. For example, blades commonly used on wind turbines and rotary aircraft must satisfy specific strength, fatigue life, damage tolerance, performance, vibration, weight, and aeroelastic stability criteria. At present, wind turbines blades and helicopter main rotor blades are largely constructed of composite materials using a spanwise single or multiple box spar design. Box beam spar designs can also include foam cores designed to prevent “oil canning,” deformation or buckling of the sheet material forming the outer skin of the rotor blade.
Current box beam spar designs are not readily improved for optimal stiffness, aeroelastic coupling, and other performance criteria, however. The structural and aeroelastic limits of box spar designs are often managed by changing the blade skin and solid core to increase stiffness and improve aeroelastic coupling. For example, biased ply lay-up techniques may be used to increase stiffness in the blade skin, or honeycomb or polyethylene cores may be used to improve stiffness and aeroelastic coupling of the blade. These features, however, provide marginal performance gains overall.
Thus, providing a rotor blade with optimal stiffness, aeroelastic stability, and performance characteristics remains a significant challenge in aeronautical engineering applications.